This invention relates to the degreasing and deoxidizing of raw aluminum foil before processing the foil into electrolytic capacitors.
Raw foil as received has both rolling oil and oxide on its surface. Both must be removed before the foil is processed to make electrolytic capacitors. The first step in capacitor processing is an etching step, where the presence of oxide scale, in particular, on the foil surface leads to preferential etching that is undesirable. Presence of rolling oil on the foil in the etching step leads to a nonuniform etch.
Foils from different sources have different amounts of oil and oxide on their surfaces. They also react differently to deoxidizing reagents. Degreasing agents have been used to remove oils followed by a deoxidizing step.
Caustic has been used in the prior art to remove oxides, but with some foils caustic has caused preferential etching. Phosphoric acid has also been used to remove oxides, but results have not been uniform.